Method for transmitting a digital signal for a marc system with a plurality of dynamic half-duplex relays, corresponding program product and relay device

Abstract

A relaying method performed by a half-duplex relay for a telecommunications system includes a reception stage of receiving codewords from sources during N uses of the transmission channel. The successive codewords correspond to B blocks, the first of which can be decoded independently of the other blocks. This stage includes a decoding step of estimating a message from each source based on received codewords. The relay performs an error detection and decision-taking step on messages decoded without error. The relay performs a stage of encoding a signal and forwarding it to a destination. The signal is representative of only messages decoded without error and includes channel encoding by an incremental redundancy code to obtain a channel encoded codeword. The relay passes from non-selective reception to selective reception after receiving B1 blocks and switches from the reception stage to the encoding and forwarding stage under control of the decision step.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a Section 371 National Stage Application of International Application No. PCT / FR2014 / 053433, filed Dec. 18, 2014, the content of which is incorporated herein by reference in its entirety, and published as WO 2015 / 092303 on Jun. 25, 2015, not in English.FIELD OF THE DISCLOSURE[0002]The field of the invention is that of transmitting encoded data in a multiple access relay channel (MARC) network. A MARC network is a telecommunications system with at least four nodes having at least two sources (transmitters), a relay, and a destination (receiver). More precisely, the invention relates to network coding and it seeks to improve the quality of data transmission, and in particular to improve the performance of error-correcting decoding in a receiver.[0003]The invention relates particularly, but not exclusively, to transmitting data via mobile networks, e.g. for real-time applications.BACKGROUND OF THE DISCLOSURE[0004]Networks...

AI Technical Summary

Benefits of technology

[0023]Below a threshold B1 for the number of uses of the transmission channel that have taken place, the relay remains in a non-selective listening mode. In this mode, the relay attempts to detect and decode without error the messages from all of the sources. As soon as a number of channel uses that have taken place exceeds the threshold B1, the relay passes into a selective listening mode. In this mode, the relay switches from a listening stage in which it attempts to detect and decode without error the messages from the sources to a stage of encoding and forwarding a message to the destination as soon as the message is decoded without error. Thus, the relay passes from non-selective listening to selective listening if the elapsed time exceeds the threshold B1, which constitutes a parameter of the system. The threshold B1 thus makes it possible to avoid penalizing sources that require more time for decoding than a source having a source-relay link that is considerably better than the source-relay links of the other sources. Setting the threshold B1 thus makes it possible to introduce operating flexibility into the MARC system that enables the relay to adapt to differing environments between the sources. B1 may be variable, e.g. for each B block codeword or as a function of some number of codewords. The listening time of the relay is not constant, unlike prior techniques that make use of a half-duplex relay in a MARC system. This flexibility makes it possible firstly to adapt to instantaneous variation in the quality of the source-relay links, which is not possible with prior art techniques. Furthermore, in the event of a link between one of the sources and the relay being very poor, lengthening the non-selective listening time can make it possible in the end for the relay to decode the source and forward a signal representative of the messages from all of the sources to the destination. Also, even if this source cannot be decoded without error, the relay can nevertheless assist the destination by forwarding a signal representative of the messages from the other sources that have been decoded without error after passing into the selective listening mode. Furthermore, this operation is completely transparent for the sources; only the relay adapts its listening mode.

[0024]Thus, the invention relies in particular on the distinction between two listening modes of the relay, a total listening mode and a selective listening mode. During the total listening mode, the relay waits to decode the messages from all of the sources without error on the basis, for any one source, of all or some of the received codewords transmitted by that source, before encoding and forwarding the messages that have been decoded without error. After passing from the total listening mode to the selective listening mode, the relay acts, after encoding, to forward the first message decoded without error. The switchover from a listening stage to an encoding and forwarding stage thus takes place dynamically and no longer at a fixed moment, as in the prior art selective relaying method. This flexibility of switchover enables the operation of the relay to be adapted to the quality of the channels between the sources and the relay, which is not possible if the listening time of the relay is constant relative to the duration of transmission from the sources.

[0025]Unlike the prior art selective relaying method, the invention distinguishes between two listening modes that increase the probability of being able to decode a plurality of sources without error even when one of the source-relay links is of quality that is much better than the other links.

[0026]The codeword that is channel encoded using an incremental redundancy code is such that among the B′ blocks transmitted successively by the relay, the accumulation of blocks from 1 to b is a codeword of a code of coding rate that decreases with b, with 1≤b≤B′. Thus, the codewords forwarded by the relay during the listening stage of another relay of the MARC system can assist that other relay in decoding a source.

[0039]The transmission by the sources takes place simultaneously over the same radio resource (time and frequency), which makes it possible to maximize use of the common spectrum resource; the source-relay links are not orthogonal. There is thus interference between the signals received by the relay and by the destination as a result of the source signals being superposed during transmission firstly between the sources and the relay and secondly between the sources and the destination. When the sources transmit simultaneously but on different spectrum resources, the relay does not need the iterative joint detection and decoding step. Under such circumstances, the relay can decode the messages from the sources on the basis of sequences received without interference between the sources.

Problems solved by technology

The transmission channel of a mobile network has the reputation of being difficult, and leads to transmission of reliability that is relatively poor.

Such reduction goes against the coverage and thus against the capacity of the system, and more generally against its performance.

Although the selective relaying technique presents undeniable advantages by avoiding error propagation by the relay, its use with a half-duplex relay has the drawback of requiring that the relay and the sources determine and know the respective durations of the two transmission stages.

There is thus interference between the signals received by the relay and by the destination as a result of the source signals being superposed during transmission firstly between the sources and the relay and secondly between the sources and the destination.

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